Micro-Electro-Mechanical Systems (MEMS) is the integration of mechanical elements, sensors, actuators, and electronics on a common substrate, such as a silicon substrate, through microfabrication technology. While the electronics are fabricated using integrated circuit (IC) process sequences (e.g., CMOS, Bipolar, or BICMOS processes), the micromechanical components are fabricated using compatible “micromachining” processes that selectively etch away parts of the silicon wafer or add new structural layers to form the mechanical and electromechanical devices.
A MEMS device includes small structures with dimensions in the micrometer scale (one millionth of a meter). Significant portions of the MEMS technology have been adopted from integrated circuit (IC) technology. For instance, similar to ICs, MEMS structures are, in general, realized in thin films of materials and patterned with photolithographic methods. Moreover, similar to ICs, MEMS structures are, in general, fabricated on a wafer by a sequence of deposition, lithography and etching.
With the increasing complexity of MEMS structures, the fabrication process of a MEMS device also becomes increasingly complex. For example, an array of MEMS probes and/or an array of MEMS interconnection pins can be assembled into a probe card. A probe card is an interface between an electronic test system and a semiconductor wafer under test. A probe card provides an electrical path between the test system and the circuitry on the wafer, thereby enabling the testing and validation of the circuitry at the wafer level, before the chips on the wafer are diced and packaged. Probes are assembled on a front side of a probe array platform. During a test, the probes form an electrical contact to the circuitry under test to make measurements. The measurements are sent, via conductive paths built in the probe platform, to the backside of the probe array platform. Interconnection pins electrically connect the backside of the probe array platform to a printed circuit board (PCB), which is connected to a test system that analyzes the measurements.
Conventionally, probes, as well as interconnection pins, are fabricated on a single substrate that has multiple layers deep in the vertical direction (with respect to the surface of the substrate), using a sequence of deposition steps across an entire wafer. A concern with the conventional methodology is that a defect or contamination occurring in any deposition step and in any individual probe may cause the entire wafer to fail. Further, the designs of probe shapes are usually restricted by the conventional processes that deposit layers of probe materials in a direction along the longitudinal axis of the probe spring. These conventional processes create the vertical, multi-dimensional structure of a probe, using multiple lithographic steps to pile and connect every layer of probe materials. As a result, the final structure (e.g., the probe spring and the pin spring) tends to have a jagged and uneven outline and lacks smooth transitions among the layers. Thus, there is a need to improve the conventional fabrication process in order to increase the yield, reduce the lead time and costs, and improve the design of the probes.